This invention relates to an improved telephone toll restrictor. More particularly, it relates to a telephone toll restrictor which splits the line during examination of tones from an instrument and utilizes a microprocessor for such examinating and for controlling the switches in the toll restrictor.
There have been provided electronic telephone toll restrictors which restrict the user from using the telephone for long distance toll calls. For example, if the number "0" were dialed, or any number of digits greater than "7" were dialed, the call would be automatically aborted by the toll restrictor by opening a switch or grounding either the tip or ring conductors.
Examples of some of prior art toll restrictors are shown in the following list of U.S. patents:
U.S. Pat. No. 3,736,383--issued May 29, 1973 PA1 U.S. Pat. No. 3,851,109--issued Nov. 26, 1974 PA1 U.S. Pat. No. 3,872,260--issued Mar. 18, 1975 PA1 U.S. Pat. No. 3,757,055--issued September, 1973 PA1 U.S. Pat. No. 3,920,936--issued Nov. 18, 1975
As can be seen from the above cited patents, most of these prior art toll restrictors provide a circuit in parallel with the telephone instrument with no mechanism for isolating the instrument from the central office. These toll restrictor circuits were preprogrammed to restrict calls based on digits dialed or tones provided from the telephone instrument. The Central Office (C.O.) must use tone receivers on all lines equipped with instruments that generate dialing tones (DTMF). Toll restrictors servicing lines equipped with DTMF instruments must also have a tone receiver. In order to provide a reliable restrictor, it is necessary for both the C.O. and toll restrictor receivers to track exactly for all dialing activity. The receiver at the C.O. and the receiver at the location of the restrictor are not at the same point in the signed path, but indeed may be separated by several miles of cable. Since the recognition characteristics of a receiver are influenced by signal amplitude, twist, background noise phase shifts, clipping, frequency delay, etc., it is not possible to guarantee that two receivers will track when the units are parallel but not at the same location.
Toll restrictors that parallel connect to the system restrict after the fact. Example: with a parallel restrictor, assume that the digit "0" is dialed. The office will receive the digit at the same time and will trunk on it. Once the office receives the digit, it will continue to process the digit. The restrictor, after it recognizes the digit "0", will attempt to restrict the call by opening the line for a period long enough to indicate to the C.O. to drop the call. This process could take as long as one second. Meanwhile, the operator phone is ringing. Should the operator answer before the C.O. times out, the operator will control the switch train and prevent it from timing out. The toll restrictor, when it reconnects to the line, allows the subscriber to get the long distance operator thereby defeating the purpose of the restrictor.
It is therefore desirable to provide an improved telephone toll restrictor which overcomes the disadvantages of the prior art.